In recent years, CDs (compact discs) are widely used as optical discs which are recording media of digital information. Optical discs using such CD systems are used in various fields, typically in audio systems and computer systems, as recording media of various types of data.
Among these optical discs using CD systems, a CD-ROM has assumed a dominant position in early stages, however, in recent years, a write-once optical disc called a CD-R (compact disc-recordable) and a rewritable optical disc called a CD-RW (compact disc-rewritable) have also been commercialized. Thus, diversification of optical discs and expansion in specification and application have dramatically increased.
In response to the commercialization of a plurality of types of optical discs, it is necessary to provide optical disc apparatuses capable of responding to the a plurality of types of optical discs as well as having compatibility with conventional optical discs.
Generally speaking, in CDs, a ratio of reflected light with respect to incident light, i.e., a reflectivity differs depending on the structure of a signal recording layer of the optical disc. Therefore, the reflected light obtained from a pickup device, i.e., the signal level of an RF signal differs depending on the type of optical disc. Using this difference in signal level, the type of optical disc, that is, CD-ROM, CD-R or CD-RW can be discriminated. The reflectivities of the respective types of optical discs are determined as follows: 0.7 or more for CD-ROM, 0.65 or more for CD-R and 0.15 to 0.25 for CD-RW.
Also, in recordable optical discs such as CD-R and CD-RW, a guide groove for tracking at the time of recording is provided, in which guide groove, time information and identification information of the optical disc, and property of the recording medium and the like are recorded as ATIP (absolute time in pre-groove) information. In particular, by reading out disc type identification information recorded as one of identification information of the disc, it is possible to discriminate the type of the optical disc between CD-R and CD-RW, for example. Furthermore, as for CD-ROM, since the ATIP information itself does not exist, it is possible to achieve type discrimination from a read-only optical disc such as CD-ROM.
In the manner as described above, it is possible to discriminate the type of optical disc. To be more specific, in the optical disc apparatus capable of responding to a plurality of types of optical discs, by making discrimination using combination of the reflectivity and the disc type identification information as described above at the time when the optical disc is loaded, which type of optical disc was loaded is discriminated.
Furthermore, on the basis of this discrimination result, the optical disc apparatus makes settings of optimum values of parameters in various kinds of servo systems such as focus servo and tracking servo and a laser power.
In the above mentioned prior art, however, since the reflected light from the optical disc varies depending on the manufacturer of the optical disc, it is difficult to determine a threshold value of quantity of reflected light for discriminating the type of optical disc by a fixed threshold value which is common among different manufacturers. For example, when an optical disc is provided by a newly entered optical disc manufacturer, there arises a case that discrimination results of the optical disc differ between the discrimination result based on the reflectivity and the discrimination result based on the disc type identification information. In such a case, the type of the optical disc is determined by giving a priority to the discrimination result based on the disc type identification information. However, it was necessary to make settings of optimum values of parameters in various kinds of servo systems such as focus servo and tracking servo and a laser power again with respect to that optical disc after the above determination.
In brief, a threshold value of quantity of reflected light for discriminating the type of optical disc is fixed regardless of the manufacture of the optical disc. For this reason, as described above, when an optical disc is loaded to the optical disc apparatus, setting of parameters of various kinds of servo systems and laser power is necessarily conducted twice, which leads the problem that the startup time of the optical disc increases.
Furthermore, when the discrimination results of the optical disc differ between the discrimination of the optical disc based on the reflectivity and the discrimination of the optical disc based on the disc type identification information, the type of the optical disc is determined by giving a priority on the latter discrimination result of the optical disc. Therefore, there is a problem that depending on the manufacturer of the optical disc, recording/reproducing operation with respect to the optical disc is carried out under the condition of erroneous discrimination result of the optical disc, so that the operation is not accurately carried out.